1. Field of the Invention
The present invention relates to magnetic gear mechanisms.
2. Description of the Related Art
In recent years, products to which a rotary machine is applied have various specifications for different purposes, such as specifications that require high torque or high-speed rotation. For example, since a wind generator has a wind turbine rotating at a few hundred r/min which is a very low speed, it is impossible to produce electricity even when the wind turbine is connected to a generator. The rotation speed has to be converted into a higher speed to produce electricity. In order to produce electricity, the wind turbine and the generator are connected by a gear to increase the rotation speed. Moreover, a transmission of an automobile is a system that converts the power produced by an engine into appropriate torque and number of revolutions arbitrarily or automatically depending on the travelling state of the automobile, and a gear is used also for this conversion. As described above, in applications to which the rotary machine is applied, the gear is widely used. In addition, most of currently used gears are mechanical gears. The mechanical gear has many practical problems such as the need for maintenance when the lubricant oil becomes insufficient or a tooth becomes chipped, high noise, and the like. It is against this background that a magnetic gear using non-contact magnetic attraction and repelling force has been studied, but an existing magnetic gear had not been put to practical use due to a small area of a portion in which magnets face each other and a low torque density. However, a magnetic flux modulated type magnetic gear has recently been proposed and a magnetic gear with a high torque density has been implemented (K. Atallah and D. Howe: A Novel High-Performance Magnetic Gear: IEEE Transactions on Magnetics, Vol. 37, No. 4, pp. 2844-2846 (hereinafter, Non-Patent Document 1)). Moreover, eddy current loss etc. in a magnetic gear has also been studied (“A Way to Improve Efficiency of Permanent-Magnet type Magnetic Gears”, Journal of the Magnetics Society of Japan Vol. 33, No. 2, 2009 (hereinafter, Non-Patent Document 2) and “Consideration of Rotor Structure in Permanent-Magnet Magnetic Gears”, Journal of the Magnetics Society of Japan Vol. 34, No. 3, 2010 (hereinafter, Non-Patent Document 3)). The technology related to positioning, a method of fixation, and improvement of strength of a group of pole pieces in a magnetic flux modulating section is described in WO 2009/087408 (hereinafter, Patent Document 1).
Non-Patent Document 1 described above introduces the principles and magnetic characteristics of a magnetic gear and does not study the mechanism and strength thereof. Moreover, in Non-Patent Documents 2 and 3 described above, eddy current loss etc. in a magnetic gear is studied, but the mechanism and strength of the magnetic gear are not studied.
On the other hand, in Patent Document 1 described above, a method by which the whole of a group of pole pieces is formed by molding, the pole pieces disposed at regular intervals in a circumferential direction, is disclosed. However, the strength is insufficient for forming the whole of a group of pole pieces by molding by using resin or the like, and consideration has to be given to cracks appearing after molding. Moreover, molding increases the number of working processes and requires longer working hours. For this reason, the above-described method has many problems from the point of view of putting this method to practical use. Likewise, in Patent Document 1 described above, a method by which an end ring is formed at an end of a group of pole pieces disposed at regular intervals in a circumferential direction and the group of pole pieces is fixed is disclosed. In this document, two methods are described. One of them is a technique of forming the end ring integrally with the group of pole pieces. The group of pole pieces is literally made of a soft magnetic material such as a magnetic steel sheet, a dust core, amorphous metal, and Permendur. Therefore, when the end ring is formed integrally with the group of pole pieces, the end ring is formed also of a magnetic substance, and a magnetic flux is likely to flow toward the end ring side. This greatly impairs the torque performance. Thus, the above-described method is undesirable. The other is a method by which an end ring is formed as a non-magnetic member and the end ring is welded to the group of pole pieces at an end thereof. In this case, only the welded area is used to maintain the strength, it is difficult to perform positioning at the time of production, and the working process becomes complicated, resulting in increased production costs.